1. Field of the Invention
The present invention relates to a touch panel and more particularly, to a touch panel in which the structure of electrodes or transparent conductive layers is improved so that equipotential lines may be uniformly spaced on a panel.
2. Description of the Related Art
Touch panels and digitizers are examples of common input devices. Input devices enable users to connect with a button shown on a display by touching or not touching the button using a finger or a penlike input means, and then to easily use information contained in a panel display device which is electrically connected to them. Of the input devices, a touch panel, which is configured in such a way to be integrated with a panel display device, is one of the input devices most suited for the current trends towards subminiature and ultralight technology such as handheld computers and a personal information terminal. There are several types of touch panels: analog resistive, digital resistive, capacitive, surface acoustic wave and infrared types.
In a touch panel, upper and lower substrates are combined with each other between which dot spacers are interposed. Upper and lower electrodes are located the upper and lower substrates, respectively. If any one point of the upper substrate is touched by an input means, the upper and lower electrodes conduct through each other. Then, a control device reads a voltage value changed by the resistance value of that point, and converts it into a digital value according to a change in an electrical potential difference to detect a position coordinate.
However, in a conventional touch panel, a voltage drop occurs from the line resistance of the upper and lower electrodes. Thus, when points which are at the same distance from the electrodes are touched, equipotential lines are not formed uniformly. For this reason, resistance for the desired position cannot be read accurately. According to a conventional art, various ways have been devised to minimize voltage drop. A widely used method is to make electrodes as wide and as thick as possible. However, this method has a disadvantage in that a restriction in the area of a touch panel limits the layout. Further, this method can only mitigate linearity but cannot remove that property completely.
To solve the above problem, it is an object of the present invention to provide a touch panel in which the shape of electrodes or transparent conductive layers is changed to minimize the line resistance of the electrodes and to form uniform equipotential lines.
Accordingly, to achieve the above object of the present invention, there is a provide a touch panel including an upper substrate over one portion of which an upper transparent conductive layer is formed, upper electrodes underlying the upper transparent conductive layer in strips, a lower substrate which is installed to face the upper substrate and on the top of which a patterned lower transparent conductive layer is formed, lower electrodes which are formed in strips so as to conduct with the lower transparent conductive layer, dot spacers which are interposed between the upper and lower substrates to maintain an interval therebetween, and a flexible printed cable which is electrically connected to the upper and lower electrodes and to which a predetermined power is applied.
One of the electrodes and the transparent conductive layers have their area formed differently in proportion to the line resistance of the electrodes so that equipotential lines may uniformly be formed between the electrodes. Further, the sectional area of the electrodes from a power application point to both ends of the left and right sides is configured to be gradually increased in proportion to the line resistance of the electrodes. In addition, the area of the transparent conductive layers from a power application point to both ends of the left and right sides in contact with the electrodes is configured to be increasingly larger in proportion to the line resistance of the electrodes.